Implant for tissue repair including chitosan

ABSTRACT

Mono- and multi-layered implants include at least one porous layer made from a freeze dried aqueous solution containing chitosan, the solution having a pH of less than about 5.

TECHNICAL FIELD

The present disclosure relates to implants, more particularly mono- ormulti-layer implants which include at least one porouschitosan-containing layer made from an aqueous solution of one or morechitosans, wherein the aqueous solution is freeze-dried at a pH of lessthan about 5.

BACKGROUND

Repairing damaged meningeal membranes has largely focused on implants(known as dural substitutes) which are grafted over damaged dura materand are designed to replace and/or regenerate the damaged tissue.Current dural substitutes based on collagen matrices provide a goodbioresorbable and safe substitute, compared to xenograft or allograftimplants. Nevertheless, dural substitutes based on collagen matrices maydisplay inferior mechanical properties such as short persistence,inferior tensile strength and low suture retention for use ininfratentorial or spine areas. Synthetic dural substitutes may showimproved mechanical and watertight properties, but generally are notabsorbable, show a lack of conformability and are less easy to use.

The present disclosure relates to biocompatible and bioresorbablechitosan based implants having enhanced mechanical properties includingincreased suture anchoring strength and increased tensile strength.These enhanced mechanical properties may be achieved by controlling thepH during processing of the implant and may eliminate the need for achemical cross-linking agent. The present matrices may be used in avariety of medical applications, including, for example surgicalimplants.

SUMMARY

Implantable structures in accordance with the present disclosure includea porous chitosan-containing layer that serves as an implant to supporttissue repair and/or tissue regeneration while providing sutureretention and a controlled and desirable time of in vivo absorption. Theporous chitosan-containing layer is made from an aqueous solution of oneor more chitosans. Control of the pH of the solution after thesolubilization of the chitosan induces changes in the solution, whichmay impact the mechanical properties of the final implant. The type ofchitosan used to make the porous layer may provide a desired in vivopersistence profile. The present implants may be used as a substitutefor and/or as a scaffold to regenerate tissue, such as, for example duramater, liver, lung, bowel, and the like.

An aspect of the invention is an implant comprising a freeze-driedporous layer derived from an aqueous solution containing chitosan, theaqueous solution having a pH of less than about 5. The aqueous solutioncontaining chitosan may comprise chitosan having a degree of acetylationranging from about 0 to about 60%. The aqueous solution containingchitosan may comprise chitosan in an amount from about 0.1 to about 10%of the solution by weight. In embodiments, the aqueous solutioncontaining chitosan comprises chitosan in an amount from about 0.8 toabout 5% of the solution by weight.

In embodiments, the pH of the aqueous solution containing chitosan isfrom about 2.5 to about 4.0, preferably from about 3.0 to about 3.5.Implants made from an aqueous solution containing chitosan at such pHshow in particular good tensile strength and good suture retention. Inembodiments, the chitosan may have a degree of acetylation of less than30%, preferably less than 20%. In particular, the chitosan porous layerof the implant of the invention shows good tensile strength when the pHof the chitosan solution is less than 4, preferably between 3 and 3.5,and when the degree of acetylation of the chitosan is less than 30%,preferably less than 20%.

In embodiments, the chitosan has a molecular weight equal to or greaterthan 304000 g/mol. In particular, the chitosan porous layer of theimplant of the invention shows good tensile strength and good sutureretention when the pH of the chitosan solution is less than 4,preferably between 3 and 3.5, and when the molecular weight of thechitosan is equal or greater than 304000 g/mol.

In embodiments, the chitosan has a degree of acetylation equal to orgreater than 10%, preferably equal to or greater than 20%.

In embodiments, the aqueous solution containing chitosan compriseschitosan in an amount from about 0.8 to 1% of the solution by weight,preferably in an amount of 1% of the solution by weight. In particular,the chitosan porous layer of the implant of the invention shows goodelongation when the degree of acetylation of the chitosan is equal orgreater than 10%, preferably equal or greater than 20%, especially whenthe concentration of the chitosan in the chitosan solution is 1% byweight.

In embodiments, the aqueous solution further comprises glycerine.

In embodiments, the aqueous solution comprises a plurality of chitosanpolymers with different degrees of acetylation.

In embodiments, the porous layer further comprises at least onebioactive agent.

In embodiments, the freeze-dried porous layer has a tensile strength ofat least about 4N. In embodiments, the freeze-dried porous layer has anelongation percentage of at least about 40%, preferably of at leastabout 60%. In embodiments, the freeze-dried porous layer has a sutureanchoring strength of at least about 0.8N. In embodiments, thefreeze-dried porous layer has a thickness of about 0.1 mm to about 10 mmin a dried state.

In embodiments, the implant further comprises a non-porous layer. Thenon-porous layer may comprise a collagen containing film. The collagenfilm may comprise a collagen selected from the group consisting ofnon-heated oxidized collagen, heated oxidized collagen, non-oxidizedheated collagen and combinations thereof. The collagen film may furthercomprise at least one macromolecular hydrophilic additive. The at leastone macromolecular additive may be selected from the group consisting ofpolyalkylene glycols, polysaccharides, oxidized polysaccharides,mucopolysaccharides, glycerin and combinations thereof.

The non-porous layer may have a thickness of less than about 100 μm in adry state.

Another aspect of the invention is a method of forming an implantcomprising:

pouring an aqueous solution containing chitosan having a pH of less thanabout 5 onto a substrate; and

forming a porous layer by freeze-drying the aqueous solution.

Pouring the aqueous solution containing chitosan may comprise pouring anaqueous solution containing chitosan, water and at least one acid.Pouring the aqueous solution containing chitosan may comprise pouring anaqueous solution containing chitosan, water and at least one acid and abioactive agent. Pouring the aqueous solution containing chitosan maycomprise pouring an aqueous solution having a pH of from about 3 toabout 3.5. Pouring the aqueous solution containing chitosan may comprisepouring an aqueous solution comprising about 1.0% chitosan by weight ofthe solution.

In embodiments, the method further comprises rinsing the porous layerwith a composition containing at least one alkaline agent. Rinsing theporous layer with a composition containing at least one alkaline agentmay comprise rinsing the porous layer with a composition containing analkaline agent selected from the group consisting of sodium hydroxide,calcium hydroxide, aluminium hydroxide, potassium hydroxide, sodiumphosphate, sodium carbonate, ammonia and combinations thereof.

In embodiments, the method may further comprise washing the rinsedporous layer. The method may further comprise freeze-drying the washedporous layer.

In embodiments, the method may further comprise at least partiallygelling a solution containing collagen; and applying the porous layeronto the at least partially gelled collagen solution.

In embodiments, the method comprises attaching the porous layer to anon-porous film comprising collagen. Attaching the porous layer to anon-porous film may comprise adhering the porous layer to the non-porousfilm using chemical bonding, photoinitiation, surgical adhesives,surgical sealants, surgical glues or combinations thereof.Alternatively, attaching the porous layer to a non-porous film maycomprise securing the porous layer to the non-porous film usingmechanical means selected from the group consisting of pins, rods,screws, staples, clips, sutures, and combinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing objects and advantages of the disclosure will become moreapparent from the reading of the following description in connectionwith the accompanying drawings, in which:

FIG. 1 is an illustration of a single-layer implant of porous chitosanin accordance with an embodiment of the present disclosure;

FIG. 2 is an illustration of a multi-layer implant including non-porousand porous layers in accordance with an embodiment of the presentdisclosure;

FIG. 3A is a scanning electron micrograph (SEM) image of a porous layerformed from a 1% concentration of a chitosan polymer solution;

FIG. 3B is a scanning electron micrograph (SEM) image of a porous layerformed from a 0.8% concentration of a chitosan polymer solution;

FIG. 4A is an SEM image of a porous layer formed from a 1% chitosansolution having the pH adjusted in accordance with an embodiment of thepresent disclosure;

FIG. 4B is an SEM image of a porous layer formed from a 0.8% chitosansolution having the pH adjusted in accordance with an embodiment of thepresent disclosure;

FIG. 5A is an SEM image of a porous layer formed from a 1% chitosansolution having the pH adjusted in accordance with an embodiment of thepresent disclosure;

FIG. 5B is an SEM image of a porous layer formed from a 0.8% chitosansolution having the pH adjusted in accordance with an embodiment of thepresent disclosure;

FIG. 6 is an SEM image of various porous chitosan layers describedherein and in accordance with the present disclosure;

FIGS. 7A and 7B show the shapes used to determine tensile strength (FIG.7A) and suture anchoring (FIG. 7B) of the implants; and

FIG. 8 is a graph of mechanical properties of implants in accordancewith the present disclosure;

FIG. 9 shows 3D diagrams representing the tensile strength (N) infunction of pH and DA for freeze-dried porous layers of implants of theinvention for a concentration in chitosan of 0.8%, respectively 1%;

FIG. 10 shows 3D diagrams representing the tensile strength (N) infunction of pH and Mw for freeze-dried porous layers of implants of theinvention for a concentration in chitosan of 0.8%, respectively 1%;

FIG. 11 shows 3D diagrams representing elongation (%) in function of pHand DA for freeze-dried porous layers of implants of the invention for aconcentration in chitosan of 0.8%, respectively 1%;

FIG. 12 shows 3D diagrams representing elongation (%) in function of pHand Mw for freeze-dried porous layers of implants of the invention for aconcentration in chitosan of 0.8%, respectively 1%;

FIG. 13 shows 3D diagrams representing suture retention (N) in functionof pH and DA for freeze-dried porous layers of implants of the inventionfor a concentration in chitosan of 0.8%, respectively 1%;

FIG. 14 shows 3D diagrams representing suture retention (N) in functionof pH and Mw for freeze-dried porous layers of implants of the inventionfor a concentration in chitosan of 0.8%, respectively 1%;

DETAILED DESCRIPTION

The present disclosure relates to implants for use in medicalapplications, such as, for example, an implant or scaffold forbiological tissue repair and/or biological tissue regeneration. Theimplant may be used in any procedure involving for example, repair orsubstitution of biological tissue. In embodiments, the implant may beused for the repair or substitution of dura mater.

The implant may be composed of one or more layers. At least one of thelayers may be a porous layer that functions, for example, as a tissuesupport during tissue regeneration. The method of forming implantsdescribed herein may provide enhanced mechanical properties, such as,for example, better suture retention strength, than matrices formed frompurified natural polymers, even when the natural polymer implant iscross-linked with chemical agents, such as formaldehydes orglutaraldehyde. These enhanced mechanical properties may be achieved bycontrolling the pH during processing of the implant and may eliminatethe need for a chemical cross-linking agent. Moreover, the sutureretention strength may be modulated by varying the concentration ofchitosan used in the formulation. Although described herein withreference to a matrix, mesh, or scaffold, the implant may be any type ofimplant suitable for allowing tissue integration.

The enhanced mechanical properties possessed by the implants inaccordance with the present disclosure may include a tensile strength ofabout 4 N (Newtons) or greater, an elongation percentage of about 60% orgreater, and/or a suture anchoring strength of about 0.8 N or greater.In embodiments, the tensile strength may be from about 4 N to about 20N, in embodiments from 10 N to about 18 N. In embodiments, theelongation percentage may be from about 60% to about 85%, in embodimentsfrom about 70% to about 80%. In embodiments, the suture anchoringstrength may be from about 0.8 N to about 1.5 N.

As stated above, the enhanced mechanical properties of the implantsdescribed herein may be due to the process used during the formation ofthe implant. During processing, an aqueous solution of chitosan is usedto form a porous layer of the implant. Chitosan solubilised in water mayhave a pH of approximately 5. It is envisioned that the chitosan may besolubilised in any water suitable for implantation including sterilewater, deionized water, distilled water, and the like.

In accordance with the present disclosure, the pH of the solubilizedchitosan may be decreased by adding a certain amount of at least oneacid until the solution has a pH under a value of about 4 in water. Itis believed that control of the pH after solubilization of the chitosaninduces a specific interaction of the chitosan polymers in solution,thereby impacting the mechanical properties of the resulting implant.

In embodiments, the implant may include more than one layer. Inembodiments, at least one of the layers is a porous chitosan-containinglayer. The layers may be bioabsorbable and may be porous or non-porous.The bioabsorbable implants may include one or more layers which arenon-porous. In embodiments, the multilayer implants may also include areinforcement layer which includes a mesh or fiber which may stiffen theporous implant. The layers of the implants described herein may beformed from the same or different biocompatible materials; at least oneof the materials may be a chitosan polymer. In embodiments, the implantmay include two or more layers, such as an implant which includes aporous chitosan layer and a non-porous collagen layer.

Chitosan, Glycosaminoglycans and Derivatives of these

Chitosan is a natural polysaccharide derived from the chitin. Chitin maybe extracted from a natural source, for example, animal tissue such assquid pens and shrimp shells, vegetable sources such as mushrooms (e.g.,“champignon de paris”), or chitin may be synthesized by modifiedmicroorganisms such as bacteria, or the chitin may be syntheticallyproduced. Derivatives of chitosan include, for example partially and/orfully deacetylated chitosan. The chitosan may have a degree ofacetylation (DA) of about 0% to about 60%. In embodiments, the chitosanmay have a degree of acetylation (DA) of about 1% to about 40%. Chitosanhaving different degrees of acetylation may be produced by aheterogeneous deacetylation process or by a homogenous reacetylatingprocess from fully deacetylated glycosaminoglycans.

The term “glycosaminoglycan” as used herein may include complexpolysaccharides having repeating units of either the same saccharidesubunit or two or more different saccharide subunits. Glycosaminoglycansmay include, for example, dermatan surfate, hyaluronic acid, chondroitinsulfates, chitin, heparin, keratan sulfate, keratosulfate, andderivatives thereof. Chitosan derivatives may include partially andfully deacetylated versions of these glycosaminoglycan compounds, suchas, deacetylated hyaluronic acid. Except in the working examples orunless otherwise indicated, as used herein the term, “chitosan” includesglycosaminoglycans, chitosan, and chitosan derivatives.

In embodiments, the chitosan has a molecular weight ranging from about100 to about 3,000,000 g/mol. In some embodiments, the chitosan has amolecular weight ranging from about 179 (chitosan monomer) to about1,000,000 g/mol. In embodiments, the chitosan also displays a lowpolydisperity index between about 1 to about 2. In embodiments, thechitosan may be a mixture of chitosans having different degrees ofacetylation. The in vivo persistence of the implant may vary dependingon the degree of acetylation of the chitosan or glycosaminoglycan usedto form the porous layer of the implant.

Porous Layer

The implants described herein include at least one porous layer madefrom an aqueous solution of chitosan, wherein the chitosan solution isfreeze-dried at a pH of less than about 5. In embodiments, the porouschitosan layer is formed by solubilizing chitosan in deionized waterwith a stoichiometric amount of acid and a chitosan polymerconcentration ranging from about 0.1% to about 10% (w/w). Thesolubilised chitosan displays a pH less than about 5 and may befreeze-dried to form a porous layer. In embodiments, the pH of theaqueous chitosan solution may be adjusted downward to a pH less thanabout 4 prior to drying. In embodiments, the chitosan polymerconcentration may be from about 0.8% to about 5.0%, in embodiments,about 1.0%.

Table 1 shows illustrative embodiments of polymer solutions suitable foruse in forming the porous chitosan layer using a freeze-drying process.

TABLE 1 Polymer pH solution concentration in before freeze Batch No.solution (w/w) drying A 1.00% 5.083 B 0.80% 5.101 C 1.00% 3.465 D 0.80%3.495 E 1.00% 3.011 F 0.80% 3.002 G 0.80% 0.960

In accordance with the present disclosure, the pH of the aqueouschitosan solution may be adjusted to a value of less than about 5. Inorder to obtain implants which display one or more enhanced mechanicalproperties as described herein, the pH of the aqueous chitosan solutionmay be specifically adjusted to a value between about 2.5 and about 4.0.In embodiments the pH of the chitosan solution may adjusted to a valuebetween about 3.0 and about 3.5.

Any pH adjusting agent, in concentrated or dilute form, may be added tothe chitosan solution to adjust the pH of the solution. Agents foradjusting pH may include acids. Some non-limiting examples acidsinclude, sulphuric acid, acetic acid, phosphoric acid, hydrochloricacid, nitric acid, formic acid, oxalic acid, citric acid, malic acid,maleic acid, adipic acid, pyruvic acid, tartaric acid and combinationsthereof. Alkalizing agents may also be used to adjust the pH and somenon-limiting examples include, hydroxides such as ammonium hydroxide,sodium hydroxide, potassium hydroxide and other bases such as sodiumcarbonate, ammonia, and sodium acetate. In embodiments, the agent foradjusting the pH of the chitosan solution may be acetic acid.

The pH adjusted solution may then freeze-dried to form a chitosan porouslayer which exhibits enhanced mechanical properties. Any suitable methodknown to those skilled in the art of freeze-drying may be used totransform the pH adjusted chitosan solution into a porous implant. Inembodiments, the pH adjusted aqueous solution of chitosan may be pouredinto an inert support, such as, for example, a flat tray made from ahydrophobic material such as PVC or polystyrene. The support containingthe chitosan solution may then be freeze-dried to form a porous layer.The resulting porous chitosan layer may exhibit enhanced mechanicalproperties.

Optionally, glycerine may be added to the aqueous chitosan solution usedto form the porous chitosan layer. When present, the concentration ofglycerine in the solution may be from about 2 to about 10 times lessthan that of the chitosan. In embodiments, the concentration ofglycerine in the solution may be less than about one-third of the amountof chitosan.

In embodiments, the porous chitosan layer may be composed of a pluralityof different chitosan monomers or polymers, wherein each of the chitosanmonomers or polymers has a different degrees of acetylation (DA).Chitosan has a degradation time related to its degree of acetylation(Kurita et al., Carbohydrate Polymers, Vol. 42 pp. 19-21, 2000; Tomihataet al., Biomaterials, Vol. 18 no. 7 pp. 567-575, 1997). A combination ofchitosan monomers or polymers with different degrees of acetylation mayproduce a porous chitosan layer having a combination of slow and fastbiodegrading chitosan. In embodiments, such a combination may beadvantageous, for example, for progressive cell colonization of theporous layer. This allows the preparation of various matrices having anadjustable in-vivo degradation profile. In embodiments, the porouschitosan layer persists at the site of implantation at least two weeksbefore being fully absorbed.

In embodiments, molecules released from the controlled degradation ofthe porous chitosan layer, may advantageously confer to the implantbiological activities, such as, for example, antimicrobial, anticancer,antioxidant, and immunostimulant effects (Kim et al., CarbohydratePolymers, Vol. 62, Issue 4, pp. 357-368, 2005) and may provide bothbiocompatibility and biodegradability, bioactive properties to theimplant. The biological properties of released chitosan oligopolymersmay also enhance tissue regeneration and extend the use of the implant,for example, to surgical sites with a high risk of contamination. Inembodiments, the degradation of a slowly biodegrading oxidized collagenlayer and a chitosan layer having a high DA, e.g., 35≦DA≦60, in vitro inthe presence of viable cells and in vivo, helps to increase theinterconnected porosity assisting in the regeneration of healthy tissue.

The porous chitosan layer may have a thickness of about 0.1 mm to about10 mm in a dried state. In multi-layer embodiments, the porous layer maybe from about 0.2 mm to about 5 mm thick in a dried state. The porouslayer displaying such a thickness may have a density of from about 0.1mg of polymer per square centimeter (length×width of the porous layer)to about 50 mg of polymer per square centimeter. In embodiments thedensity of the porous layer may range from about 0.25 mg of polymer persquare centimeter to about 20 mg of polymer per square centimeter.

The size of the pores in such a porous layer can be from about 10 μm toabout 1000 μm, in embodiments from about 50 μm to about 500 μm. Theporous layer may be optionally compacted by using a press or any otherappropriate means, so as to obtain a thickness comprised between 0.1 mmand 5 mm, and in some embodiments between about 0.1 mm and about 3 mm.

Non-Porous Layer Formation

In some embodiments, the implants described herein may be multi-layered.The additional layers may be porous or non-porous layers ofbiocompatible materials. In embodiments, the multi-layered implant mayinclude a porous layer as described herein and a non-porous layerattached thereto. The non-porous layer may be, for example, abiodegradable film. The biodegradable film may be made from anybiocompatible material suitable for implantation. The biocompatiblematerial may be bioabsorbable. In embodiments, a non-porous layer mayprevent the implant from adhering to the surrounding tissue and minimizethe leakage of any physiological fluid.

In embodiments, the non-porous layer may include collagen and/orcollagen derivatives. In embodiments, the collagen films may furtherinclude a macromolecular compound, such as, for example, polyethylene,glycerol and combinations thereof. Suitable collagen films may be madefrom non-heated oxidized collagen, heated oxidized collagen,non-oxidized heated collagen or combinations thereof. In embodiments,the collagen film may be made from heated oxidized collagen, asdescribed in U.S. Pat. No. 6,596,304, the entire disclosure of which isincorporated herein by reference.

Table 2 gives illustrative concentrations of collagen solutions usefulin forming a non-porous layer.

TABLE 2 Non heated oxidized collagen content 0.1%-3% (w/w) HeatedOxidized collagen content 0.1%-6% (w/w) Heated collagen content 0.1%-6%(w/w)

In embodiments, at least one macromolecular hydrophilic additive that ischemically unreactive with the collagen may be added to the solutionused to form the non-porous layer. “Chemically unreactive with thecollagen” as used herein means a hydrophilic compound which is notlikely to form covalent bonds with collagen.

The macromolecular hydrophilic additive advantageously may have amolecular weight in excess of 3,000 Daltons, in embodiments from about3,000 to about 20,000 Daltons. Illustrative examples of suitablemacromolecular hydrophilic additives include polyalkylene glycols (suchas polyethylene glycol), polysaccharides (e.g., starch, dextran and/orcellulose), oxidized polysaccharides, and mucopolysaccharides. It shouldof course be understood that combinations of macromolecular hydrophilicadditives may be used. The concentration of hydrophilic additive(s) maytypically be from about 2 to about 10 times less than that of thecollagen.

Following implantation, the macromolecular hydrophilic additive may beeliminated by diffusion through the non-porous layer, in a few days. Theswelling of the macromolecular hydrophilic additive may advantageouslypromote degradation of a collagenic non-porous layer in less than aboutone month in situ.

In embodiments, glycerine may be combined with the collagen to form thenon-porous layer. When present, the concentration of glycerine in thesolution may be from about 2 to about 10 times less than theconcentration of collagen. In embodiments, the concentration ofglycerine in the solution may be less than about one-third of thecollagen concentration.

In embodiments, solutions used to form the non-porous layer include, forexample, from about 0.1 to about 3% w/w of non-heated oxidized collagen,up to 2% w/w polyethylene glycol and up to 1% w/w glycerol. In the drystate, the resulting non-porous layer may contain from about 40 to about100% w/w of non-heated oxidized collagen, up to 60% w/w polyethyleneglycol and up to 20% w/w glycerol.

In embodiments, solutions for forming the non-porous layer may includefrom about 0.5 to about 1.5% w/w of non-heated oxidized collagen, fromabout 0.6 to about 0.9% w/w polyethylene glycol and from about 0.3 toabout 0.6% w/w glycerol. In the dry state, the resulting non-porouslayer may contain from about 60 to about 90% w/w of non-heated oxidizedcollagen, from about 15 to about 30% w/w polyethylene glycol and fromabout 5 to about 15% w/w glycerol.

Other examples of solutions useful in forming the non-porous layerinclude from about 0.1 to about 3% w/w of heated oxidized collagen, fromabout 0.1 to about 3% w/w of heated collagen, up to 2% w/w polyethyleneglycol and up to 1% w/w glycerol. In the dry state, the resultingnon-porous layer may contain from about 40 to about 100% w/w of heatedoxidized collagen, about 40 to about 100% w/w of heated collagen, up to60% w/w polyethylene glycol and up to 20% w/w glycerol.

In embodiments, solutions useful in forming the non-porous layer includefrom about 0.5 to about 1.5% w/w of non-heated oxidized collagen, fromabout 0.5 to about 1.5% w/w of heated collagen, from about 0.6 to about0.9% w/w polyethylene glycol and from about 0.3 to about 0.6% w/wglycerol. In the dry state, the resulting non-porous layer may containfrom about 60 to about 90% w/w of heated oxidized collagen, from about60 to about 90% w/w of heated collagen, from about 15 to about 30% w/wpolyethylene glycol and from about 5 to about 15% w/w glycerol.

The thickness of the non-porous layer may be less than about 100 μmthick, and in embodiments may range from about 15 μm to about 75 μmthick in a dry state.

Any bioactive agent, which may enhance tissue repair or limit the riskof sepsis, and/or any chemical additive (e.g., glycerol, 1-2 propandiol)which may modulate the mechanical properties (swelling rate in water,tensile strength and the like) of the film may be added during thepreparation of the non-porous film formulation.

Bioactive Agents

In embodiments, at least one bioactive agent may be combined with one ormore layers of the implant. In these embodiments, the implant may serveas a vehicle for delivery of the bioactive agent. The term “bioactiveagent” as used herein, is used in its broadest sense and includes anysubstance or mixture of substances that have clinical use. Consequently,bioactive agents may or may not have pharmacological activity per se,e.g., a dye, or fragrance. In embodiments, a bioactive agent may be anagent that provides a therapeutic or prophylactic effect, a compoundthat effects or participates in tissue growth, cell growth, celldifferentiation, an anti-adhesive compound, a compound that may be ableto invoke a biological action such as an immune response, or could playany other role in one or more biological processes. It is envisionedthat the bioactive agent may be applied to any portion of the implant inany suitable form of matter, e.g., films, powders, liquids, gels and thelike.

Examples of classes of bioactive agents which may be utilized inaccordance with the present disclosure include anti-adhesives,antimicrobials, analgesics, antipyretics, anesthetics, antiepileptics,antihistamines, anti-inflammatories, cardiovascular drugs, diagnosticagents, sympathomimetics, cholinomimetics, antimuscarinics,antispasmodics, hormones, growth factors, muscle relaxants, adrenergicneuron blockers, antineoplastics, immunogenic agents,immunosuppressants, gastrointestinal drugs, diuretics, steroids, lipids,lipopolysaccharides, polysaccharides, and enzymes. It is also intendedthat combinations of bioactive agents may be used.

Anti-adhesive agents can be used to prevent adhesions from formingbetween the implant and the surrounding tissues opposite the targettissue. In addition, anti-adhesive agents may be used to preventadhesions from forming between the present implant and the packagingmaterial. Some examples of these agents include, but are not limited topoly(vinyl pyrrolidone), carboxymethyl cellulose, hyaluronic acid,polyethylene oxide, poly vinyl alcohols and combinations thereof.

Suitable antimicrobial agents which may be included as a bioactive agentin the implant of the present disclosure include triclosan, also knownas 2,4,4′-trichloro-2′-hydroxydiphenyl ether, chlorhexidine and itssalts, including chlorhexidine acetate, chlorhexidine gluconate,chlorhexidine hydrochloride, and chlorhexidine sulfate, silver and itssalts, including silver acetate, silver benzoate, silver carbonate,silver citrate, silver iodate, silver iodide, silver lactate, silverlaurate, silver nitrate, silver oxide, silver palmitate, silver protein,and silver sulfadiazine, polymyxin, tetracycline, aminoglycosides, suchas tobramycin and gentamicin, rifampicin, bacitracin, neomycin,chloramphenicol, miconazole, quinolones such as oxolinic acid,norfloxacin, nalidixic acid, pefloxacin, enoxacin and ciprofloxacin,penicillins such as oxacillin and pipracil, nonoxynol 9, fusidic acid,cephalosporins, and combinations thereof. In addition, antimicrobialproteins and peptides such as bovine lactoferrin and lactoferricin B andantimicrobial polysaccharides such as fucans and derivatives may beincluded as a bioactive agent in the implants of the present disclosure.

Other bioactive agents which may be included in the implant of thepresent disclosure include: local anesthetics; non-steroidalantifertility agents; parasympathomimetic agents; psychotherapeuticagents; tranquilizers; decongestants; sedative hypnotics; steroids;sulfonamides; sympathomimetic agents; vaccines; vitamins; antimalarials;anti-migraine agents; anti-parkinson agents such as L-dopa;anti-spasmodics; anticholinergic agents (e.g., oxybutynin);antitussives; bronchodilators; cardiovascular agents such as coronaryvasodilators and nitroglycerin; alkaloids; analgesics; narcotics such ascodeine, dihydrocodeinone, meperidine, morphine and the like;non-narcotics such as salicylates, aspirin, acetaminophen,d-propoxyphene and the like; opioid receptor antagonists, such asnaltrexone and naloxone; anti-cancer agents; anti-convulsants;anti-emetics; antihistamines; anti-inflammatory agents such as hormonalagents, hydrocortisone, prednisolone, prednisone, non-hormonal agents,allopurinol, indomethacin, phenylbutazone and the like; prostaglandinsand cytotoxic drugs; estrogens; antibacterials; antibiotics;anti-fungals; anti-virals; anticoagulants; anticonvulsants;antidepressants; antihistamines; and immunological agents.

Other examples of suitable bioactive agents that may be included inaccordance with the present disclosure include, viruses and cells,peptides, polypeptides and proteins, analogs, muteins, and activefragments thereof, such as immunoglobulins, antibodies, cytokines (e.g.,lymphokines, monokines, chemokines), blood clotting factors, hemopoieticfactors, interleukins (e.g., IL-2, IL-3, IL-4, IL-6), interferons (e.g.,3-IFN, a-IFN, y-IFN), erythropoietin, nucleases, tumor necrosis factor,colony stimulating factors (e.g., GCSF, MCSF), insulin, anti-tumoragents and tumor suppressors, blood proteins, gonadotropins (e.g., FSH,LH, CG, etc.), hormones and hormone analogs (e.g., growth hormone),vaccines (e.g., tumoral, bacterial and viral antigens); somatostatin;antigens; blood coagulation factors; growth factors (e.g., nerve growthfactor, insulin-like growth factor); protein inhibitors, proteinantagonists, and protein agonists; nucleic acids, such as antisensemolecules, DNA and RNA; oligonucleotides; polynucleotides; andribozymes.

Formation of Mono- and Multi-Layer Matrices

With reference to FIG. 1, implant 15 may be formed from a single porouschitosan layer 10, having a thickness 12. As shown in FIG. 2, implant 25may be multi-layer, for example, a porous chitosan layer 20 may becoated with a non-porous layer 22 to form implant 25 having a thickness24.

As stated above, although described herein with reference to a implant,the implant may be any type of scaffold, implant, and the like. When theimplant described herein is multilayer, the implant may be formed usingany method known to those skilled in the art capable of connecting anon-porous layer to a porous layer. It is envisioned that the non-porouslayer and the porous layer may be adhered to one another using chemicalbonding, surgical adhesives, surgical sealants, and surgical glues. Inaddition, the layers may be bound together using mechanic means such aspins, rods, screws, clips, sutures, staples, etc. Still further, thelayers may naturally or through chemical or photoinitiation, interactand crosslink or provide covalent bonding between the layers.

In embodiments, a multilayer implant may be prepared by attaching theindividual layers of materials together to form a multiple layerimplant. The porous layer may be formed separate and apart from thenon-porous layer. Alternatively, the porous and non-porous layers may beformed together. In embodiments, a two-layer implant may be prepared byfirst pouring a solution for a non-porous layer into an inert support ormold and distributing the solution for a non-porous layer evenly. Thissolution may be left to gel by the removal of solvent and cooling.

In embodiments, the mold or support is inert in that it does not reactwith the solution or the solutions constituents. The support mayadvantageously be made from a hydrophobic material such as, for example,PVC or polystyrene. However, this support may also consist of astrippable material, which may remain slightly adhesive and which maythen be separated from the implant at the time of surgical use. Thesupport may also consist of a film, for example dried collagen or alayer of collagenic material gel in a more advanced state of gellation,onto which the solution may be poured.

The density of the non-porous layer initially applied as a solution tothe support may be from about 0.1 g solution/cm² to about 0.3 gsolution/cm². This solution advantageously may be poured at atemperature from about 4° C. to about 30° C., and in embodiments fromabout 18° C. to about 25° C. Once applied to the support, the solutionis allowed to partially gel. Partial gelling results from cooling of thesolution, and not from drying of the solution. This solution may be leftto gel and a porous layer previously prepared may be applied to thesolution during gellation.

Application of the porous layer onto the partially gelled non-poroussolution means placing the porous layer onto the gel, and optionallyapplying slight pressing. The pressing should be insufficient to causeany significant compaction of the porous layer.

The moment at which the porous layer is applied to the solution duringgellation may depend upon the nature of the solution employed, theconditions under which the solution is maintained during gellation andthe nature of the porous layer. Generally, the solution may be allowedto gel for a period of time prior to application of the porous layer,such that the gel is still soft and allows the porous layer to penetrateover a distance, which is advantageously from about 0.05 mm to about 2mm and, in embodiments from about around 0.1 mm to about 0.5 mm. Theappropriate moment for application of the porous layer for any givencombination of materials/conditions may be determined empirically, forexample by applying small samples of the porous layer to the gel atvarious times and evaluating the degree of penetration and adherence.Generally, when the solution, which is gelling, is at a temperature ofbetween 4° C. and 30° C., the porous layer may be applied about 5 toabout 30 minutes after the solution has been poured over the supportholding it.

The composite layers may be left to dry or dried in order to obtain thefinal implant. When the solution used to form the non-porous filmincludes oxidized collagen, it may be polymerized while the material isdrying. This drying may occur at a temperature of from about 4° C. toabout 30° C. In embodiments, the drying may occur at a temperature fromabout 18° C. to about 25° C. The material may be dried in a jet ofsterile air.

After drying, the implant may be separated from its support, packagedand sterilized using conventional techniques, e.g., irradiation withbeta (electronic irradiation) or gamma (irradiation using radioactivecobalt) rays.

The present implants may be stable at ambient temperature and may remainstable for long enough periods of time to be handled at temperatureswhich may rise to about 37° C. to about 40° C. In accordance with thepresent disclosure, implants may be produced at any desired size or inlarge sheets later cut to sizes appropriate for the envisionedapplication.

The present implants may be implanted using open surgery or in alaparoscopic procedure. When implanted laparoscopically, the presentimplants may be rolled with the porous side on the inside, before trocarinsertion.

The following non-limiting example illustrates the preparation ofimplants in accordance with the present disclosure.

EXAMPLES

Porous chitosan layers useful as a mono-layer implant or as part of amulti-layer implant were prepared as follows:

Example 1 Chitosan Polymer Concentration 1%, Freeze-Dried at a pH of 5

A chitosan porous layer was prepared as follows: 1.21 g of chitosan (DA2.5%) was solubilized in sterile water including a stoichiometric amountof acetic acid (0.437 g) over 6 hours until a 1% w/w solution wasobtained. The pH of the chitosan solution was measured to be about 5.1.The aqueous chitosan solution was poured into a 12×17 cm mold andfreeze-dried for 28 hours. The porous layer was then rinsed in analkaline solution for 5 minutes, followed by being washed in sterilewater until the pH of the porous layer was neutral. The neutral porouslayer was then freeze-dried a second time to provide the porous layerfor implantation.

FIG. 3A is an SEM image of the porous implant formed from a 1% chitosansolution which was freeze-dried at a pH of 5.

Example 2 Chitosan Polymer Concentration 0.8%, Freeze-Dried at a pH of 5

A chitosan porous layer was prepared as follows: 0.97 g of chitosan (DA2.5%) was solubilized in sterile water containing a stoichiometricamount of acetic acid (0.350 g) for 6 hours until a solution at 0.8% w/wwas obtained. At this stage, the pH of the chitosan solution wasmeasured to be about 5.1. The aqueous chitosan solution was poured intoa 12×17 cm mold and freeze-dried for 28 hours. The porous layer was thenrinsed in an alkaline solution for 5 minutes, followed by being washedin sterile water until the pH of the porous layer was neutral. Theneutral porous layer was then freeze-dried a second time to provide theporous layer for implantation.

FIG. 3B is an SEM image of the porous implant formed from a 0.8%chitosan solution which was freeze-dried at a pH of 5.

Example 3 Chitosan Polymer Concentration 1%, pH 3.5

A chitosan porous layer was prepared as follows: 1.24 g of chitosan (DA2.5%) was solubilized in sterile water containing a stoichiometricamount of acetic acid (0.448 g) for 6 hours to obtain a 1.025% w/wsolution. The pH of the chitosan solution was adjusted to 3.5 by adding3 ml of acetic acid and the blend (a polymer concentration of 1%) wascentrifuged. The final pH of the chitosan solution was 3.5. The aqueouschitosan solution was poured into a 12×17 cm mold and freeze-dried for28 hours. The porous layer was then rinsed in an alkaline solution for 5minutes, followed by being washed in sterile water until the pH of theporous layer was neutral. The neutral porous layer was then freeze-drieda second time to provide the porous layer for implantation.

FIG. 4A is an SEM image of the porous implant formed from a 1% chitosansolution which was freeze-dried at a pH of 3.5.

Example 4 Chitosan Polymer Concentration 0.8%, pH 3.5

A chitosan porous layer was prepared as follows: 0.99 g of chitosan (DA2.5%) was solubilized in sterile water containing a stoichiometricamount of acetic acid (0.358 g) for 6 hours to obtain a 0.82% w/wsolution. The pH of the solution was adjusted to 3.5 by adding 2.4 ml ofacetic acid and the blend (new polymer concentration of 0.8%) wascentrifuged. The final pH of the chitosan solution was 3.5. The aqueouschitosan solution was poured into a 12×17 cm mold and freeze-dried for28 hours. The porous layer was then rinsed in an alkaline solution for 5minutes, followed by being washed in sterile water until the pH of theporous layer was neutral. The neutral porous layer was then freeze-drieda second time to provide the porous layer for implantation.

FIG. 4B is an SEM image of the porous implant formed from a 0.8%chitosan solution which was freeze-dried at a pH of 3.5.

Example 5 Chitosan Polymer Concentration 1%, pH 3

A chitosan porous layer was prepared as follows: 1.32 g of chitosan (DA2.5%) was solubilized in sterile water containing a stoichiometricamount of acetic acid (0.477 g) for 6 hours to obtain a 1.09% w/wsolution. The pH of the solution was adjusted to 3 by adding 10.9 ml ofacetic acid and the blend (new polymer concentration of 1%) wascentrifuged. The final pH of the chitosan solution was 3.0. The aqueouschitosan solution was poured into a 12×17 cm mold and freeze-dried for28 hours. The porous layer was then rinsed in an alkaline solution for 5minutes, followed by being washed in sterile water until the pH of theporous layer was neutral. The neutral porous layer was then freeze-drieda second time to provide the porous layer for implantation.

FIG. 5A is an SEM image of the porous implant formed from a 1% chitosansolution which was freeze-dried at a pH of 3.

Example 6 Chitosan Polymer Concentration 0.8%, pH 3

A chitosan porous layer was prepared as follows: 1.06 g of chitosan (DA2.5%) was solubilized in sterile water containing a stoichiometricamount of acetic acid (0.382 g) for 6 hours to obtain a 0.87% w/wsolution. The pH of the solution was adjusted to 3 by adding 8.7 ml ofacetic acid and the blend (new polymer concentration of 0.8%) wascentrifuged. The final pH of the chitosan solution was 3.0. The aqueouschitosan solution was poured into a 12×17 cm mold and freeze-dried for28 hours. The porous layer was then rinsed in an alkaline solution for 5minutes, followed by being washed in sterile water until the pH of theporous layer was neutral. The neutral porous layer was then freeze-drieda second time to provide the porous layer for implantation.

FIG. 5B is an SEM image of the porous implant formed from a 0.8%chitosan solution which was freeze-dried at a pH of 3.

Example 7 Chitosan Polymer Concentration 0.8%, pH 1

A chitosan porous layer was prepared as follows: 1.06 g of chitosan (DA2.5%) was solubilized in sterile water containing a stoichiometricamount of acetic acid (0.382 g) for 6 hours to obtain a 0.87% w/wsolution. The pH of the solution was adjusted to 1 by adding 8.7 ml ofacetic acid and hydrochloric acid, and the blend (new polymerconcentration of 0.8%) was centrifuged. The final pH of the chitosansolution was 0.96. The aqueous chitosan solution was poured into a 12×17cm mold and freeze-dried for 28 hours. The porous layer was then rinsedin an alkaline solution for 5 minutes, followed by being washed insterile water until the pH of the porous layer was neutral. The neutralporous layer was then freeze-dried a second time to provide the porouslayer for implantation.

Thickness of Resulting Matrices

FIG. 6 includes SEM photos of each of the matrices resulting fromsolutions of examples 1-6 at 500 μm. The adjustment of the pH within thesolution prior to freeze-drying modified the final thickness, after theneutralization step, of the resulting implant. As seen in FIG. 6, thelower the pH of the solution, the smaller the thickness of the resultingporous layer.

Tensile Strength and Suture Anchoring

The evolution of the strength at break of the porous layer was evaluatedagainst the initial pH of the solution. The samples of porous layer werecut into the desired shape and length as illustrated below:

The shape shown in FIG. 7A was used to test the tensile strength and theshape shown in FIG. 7B was used to determine suture anchoring. Prior totesting, the samples were hydrated in sterile water for 5 min.

Parameters of the mechanical testing:

-   -   Tensile speed: 50 mm/min    -   L(0) (for tensile test): 40 mm    -   Cell force: 100 N, no 25943 (tensile test) and 25 N (suture        test)

Table 3 contains the results for both the amount of elongation and forcerequired to reach the breaking point of the implant. Table 4demonstrates the amount of force and elongation of the implant prior tothe suture detaching from the implant.

TABLE 3 Elongation # Samples Implant Force R (N) R (%) Tested Example 1 3.64 ± 0.74 53.9 ± 7.5 8 Example 2  2.41 ± 0.73 43.6 ± 6.4 8 Example 310.21 ± 2.14  69.7 ± 11.8 8 Example 4 13.07 ± 2.07 80.5 ± 4.0 5 Example5 18.17 ± 2.38 73.0 ± 6.2 8 Example 6 11.64 ± 2.81 66.1 ± 8.6 8 Example7  9.19 ± 1.99 19.5 ± 3.1 8

TABLE 4 Elongation # Samples Implant Force R (N) R (%) Tested Example 10.73 ± 0.07 14.1 ± 2.8 8 Example 2 0.56 ± 0.08 13.8 ± 3.6 8 Example 31.19 ± 0.11 16.1 ± 2.4 8 Example 4 1.25 ± 0.27 14.7 ± 4.1 6 Example 51.43 ± 0.24 14.1 ± 3.7 8 Example 6 1.05 ± 0.26 13.9 ± 3.6 8 Example 70.20 ± 0.09  5.0 ± 4.5 7

A comparison of the pH and the tensile strength of the implants areshown in FIG. 8. The pH of the chitosan solution prior to freeze-dryingaltered the mechanical properties of the porous layer. Irrespective ofthe polymer concentration, the pH creating the maximal strength at breakis between 3 and 3.5. This tendency is slightly different between thetwo polymer concentrations tested. Therefore, density may not be theonly the cause of the mechanical properties increased of the porouslayer. Without wishing to be bound to any theory, it is believed thatthe variation of the pH may alter polymer chain orientation due tocharge density variation along the polymer chain or deviation of thebalance of the hydrophilic/hydrophobic interaction.

With respect to the polymer concentration, the greater the polymerconcentration, the more polymer chain mobility is affected. Therearrangement of the polymer chain caused by pH variation requiredhigher constraint resulting in a shift of the maximal strength at breakat lower pH value as compared to the porous layer with 0.8% polymerconcentration.

The effect of initial polymer concentration of the solution was apparentwhen the pH dropped below 2. The resulting porous layer showed anon-homogeneous structure especially at a polymer concentration of about1.0% (w/w). The variation of the pH in the solution inducesmodifications within the structure of the final porous layer.

Example 8

Chitosan Porous Layers have been Prepared According to the SameManufacturing method as described in Example 1 but with the followingvarying parameters:

-   -   1) Concentration of chitosan in the aqueous chitosan solution        (Cp): two different concentrations were tested: Cp=0.8% by        weight, and Cp=1% by weight    -   2) Degree of acetylation of the chitosan used (DA): five        different degrees of acetylation were tested: DA=2%, DA=10%,        DA=20%, DA=30% and DA=40%    -   3) Molecular weight of the chitosan used: four different        molecular weights were tested: Mw=113000 g/mol, Mw=304000 g/mol,        Mw=380500 g/mol and Mw=420000 g/mol.    -   4) pH of the chitosan solution: four different pH were tested:        pH=3, pH=3.5, pH=4 and pH=5.

The tensile strength, the elongation and the suture retention weretested for all chitosan porous layers thus prepared. The tests wereperformed on an extensometer Hounsfield ref H5KS equipped with a 100Ncell. The tests were completed according to the following procedures:

1) Tensile strength and elongation: samples cut at 8×2.5 cm are preparedand hydrated. Each sample is maintained into pneumatic jaws andextension is performed at 50 mm/min till sample ruptures. Data arerecorded with a 100N cell as shown on FIG. 7A. Maximum tensile strengthto rupture is recorded, as well as maximum elongation to rupture.2) Suture retention: the test consists in introducing a suturing yarn(Surgipro II 5-0) into a 4×4 cm sample S as shown on FIG. 7B. The bottomof the sample is maintained into jaws and the yarn is then pulled in thetop direction at 50 mm/min till complete shearing of the sample. Maximumtensile strength of suture retention is recorded.

The results are shown in FIGS. 9-14.

FIG. 9 shows 3D diagrams representing the tensile strength (N) for thechitosan porous layers of the present example for a concentration inchitosan of 0.8%, respectively 1%, where the pH varies from 3 to 5 asdescribed above, and where the DA varies from 2% to 40% as describedabove; in such cases, the molecular weight of the chitosan varies infunction of the DA as follows: for DA equal to 2%, Mw is around 425000g/mol; for DA equal to 10, 20 or 40%, Mw is around 513000 g/mol.

FIG. 10 shows 3D diagrams representing the tensile strength (N) for thechitosan porous layers of the present example for a concentration inchitosan of 0.8%, respectively 1%, and where the pH varies from 3 to 5as described above and where the molecular weight (Mw) of the chitosanvaries from 113000 to 420000 g/mol as described above. In such cases,the DA of the chitosans used is equal to 2%.

As appears from these Figures, the tensile strength of the chitosanporous layers of the present example increases when the pH of thechitosan solution decreases. In particular, the chitosan porous layersshow good tensile strength when the pH of the chitosan solution is fromabout 3 to about 3.5. In particular, with reference to FIG. 9, thechitosan porous layers of the present example show good tensile strengthwhen the pH of the chitosan solution is less than 4, preferably between3 and 3.5, and when the degree of acetylation of the chitosan is lessthan 30%, preferably less than 20%. With reference to FIG. 10, thechitosan porous layers of the present example show good tensile strengthwhen the pH of the chitosan solution is less than 4, preferably between3 and 3.5, and when the molecular weight of the chitosan is equal orgreater than 304000 g/mol.

FIG. 11 shows 3D diagrams representing the elongation (%) for thechitosan porous layers of the present example for a concentration inchitosan of 0.8%, respectively 1%, where the pH varies from 3 to 5 asdescribed above, and where the DA varies from 2% to 40% as describedabove; in such cases, the molecular weight of the chitosan varies infunction of the DA as follows: for DA equal to 2%, Mw is around 425000g/mol; for DA equal to 10, 20 or 40%, Mw is around 513000 g/mol.

FIG. 12 shows 3D diagrams representing the elongation (%) for thechitosan porous layers of the present example for a concentration inchitosan of 0.8%, respectively 1%, and where the pH varies from 3 to 5as described above and where the molecular weight (Mw) of the chitosanvaries from 113000 to 420000 g/mol as described above. In such cases,the DA of the chitosans used is equal to 2%.

As appears from these Figures, the chitosan porous layers of the presentexample show good elongation when the degree of acetylation of thechitosan is equal or greater than 10%, preferably equal or greater than20%, especially when the concentration of the chitosan in the chitosansolution is 1% by weight.

FIG. 13 shows 3D diagrams representing the suture retention (N) for thechitosan porous layers of the present example for a concentration inchitosan of 0.8%, respectively 1%, where the pH varies from 3 to 5 asdescribed above, and where the DA varies from 2% to 40% as describedabove; in such cases, the molecular weight of the chitosan varies infunction of the DA as follows: for DA equal to 2%, Mw is around 425000g/mol; for DA equal to 10, 20 or 40%, Mw is around 513000 g/mol.

FIG. 14 shows 3D diagrams representing the suture retention (N) for thechitosan porous layers of the present example for a concentration inchitosan of 0.8%, respectively 1%, and where the pH varies from 3 to 5as described above and where the molecular weight (Mw) of the chitosanvaries from 113000 to 420000 g/mol as described above. In such cases,the DA of the chitosans used is equal to 2%.

As appears from these Figures, the suture retention of the chitosanporous layers of the present example increases when the pH of thechitosan solution decreases. In particular, the chitosan porous layersof the present example show good suture retention when the pH of thechitosan solution is less than 4, preferably between 3 and 3.5, and whenthe molecular weight of the chitosan is equal or greater than 304000g/mol.

While the above description contains many specifics, these specificsshould not be construed as limitations on the scope of the presentdisclosure, but merely as exemplifications of preferred embodimentsthereof. Those skilled in the art will envision many other possiblevariations that are within the scope and spirit of the presentdisclosure.

What is claimed is:
 1. An implant comprising a freeze-dried porous layerderived from an aqueous solution containing chitosan, the aqueoussolution having a pH of less than about
 5. 2. The implant of claim 1wherein the aqueous solution containing chitosan comprises chitosanhaving a degree of acetylation ranging from about 0 to about 60%.
 3. Theimplant of claim 1 or 2 wherein the aqueous solution containing chitosancomprises chitosan in an amount from about 0.1 to about 10% of thesolution by weight.
 4. The implant of claim 3 wherein the aqueoussolution containing chitosan comprises chitosan in an amount from about0.8 to about 5% of the solution by weight.
 5. The implant of any one ofclaims 1-4 wherein the pH of the aqueous solution containing chitosan isfrom about 2.5 to about 4.0.
 6. The implant of claim 5 wherein the pH ofthe aqueous solution containing chitosan is from about 3.0 to about 3.5.7. The implant of claim 5 or 6, wherein the chitosan has a degree ofacetylation of less than 30%, preferably less than 20%.
 8. The implantof claim 5 or 6, wherein the chitosan has a molecular weight equal to orgreater than 304000 g/mol.
 9. The implant of any one of claim 1-6 or 8,wherein the chitosan has a degree of acetylation equal to or greaterthan 10%, preferably equal to or greater than 20%.
 10. The implant ofany one of claims 1-9, wherein the aqueous solution containing chitosancomprises chitosan in an amount from about 0.8 to 1% of the solution byweight, preferably in an amount of 1% of the solution by weight.
 11. Theimplant of any one of claims 1-10 wherein the aqueous solution furthercomprises glycerin.
 12. The implant of any one of claims 1-11 whereinthe aqueous solution comprises a plurality of chitosan polymers withdifferent degrees of acetylation.
 13. The implant of any one of claims1-12 wherein the porous layer further comprises at least one bioactiveagent.
 14. The implant of any one of claims 1-13 wherein thefreeze-dried porous layer has a tensile strength of at least about 4N.15. The implant of any one of claims 1-14 wherein the freeze-driedporous layer has an elongation percentage of at least about 40%,preferably of at least about 60%.
 16. The implant of any one of claims1-15 wherein the freeze-dried porous layer has a suture anchoringstrength of at least about 0.8N.
 17. The implant of any one of claims1-16 wherein the freeze-dried porous layer has a thickness of about 0.1mm to about 10 mm in a dried state.
 18. The implant of any one of claims1-17 further comprising a non-porous layer.
 19. The implant of claim 18wherein the non-porous layer comprises a collagen containing film. 20.The implant of claim 19 wherein the collagen film comprises a collagenselected from the group consisting of non-heated oxidized collagen,heated oxidized collagen, non-oxidized heated collagen and combinationsthereof.
 21. The implant of claim 19 or 20 wherein the collagen filmfurther comprises at least one macromolecular hydrophilic additive. 22.The implant of claim 21 wherein the at least one macromolecular additiveis selected from the group consisting of polyalkylene glycols,polysaccharides, oxidized polysaccharides, mucopolysaccharides, glycerinand combinations thereof.
 23. The implant of any one of claims 18-22wherein the non-porous layer has a thickness of less than about 100 μmin a dry state.
 24. A method of forming an implant comprising: pouringan aqueous solution containing chitosan having a pH of less than about 5onto a substrate; and forming a porous layer by freeze-drying theaqueous solution.
 25. A method as in claim 24 wherein pouring theaqueous solution containing chitosan comprises pouring an aqueoussolution containing chitosan, water and at least one acid.
 26. A methodas in claim 25 wherein pouring the aqueous solution containing chitosancomprises pouring an aqueous solution containing chitosan, water and atleast one acid and a bioactive agent.
 27. A method as in any one ofclaims 24-26 wherein pouring the aqueous solution containing chitosancomprises pouring an aqueous solution having a pH of from about 3 toabout 3.5.
 28. A method as in any one of claims 24-27 wherein pouringthe aqueous solution containing chitosan comprises pouring an aqueoussolution comprising about 1.0% chitosan by weight of the solution. 29.The method of any one of claims 24-28 further comprising rinsing theporous layer with a composition containing at least one alkaline agent.30. The method of claim 29 wherein rinsing the porous layer with acomposition containing at least one alkaline agent comprises rinsing theporous layer with a composition containing an alkaline agent selectedfrom the group consisting of sodium hydroxide, calcium hydroxide,aluminium hydroxide, potassium hydroxide, sodium phosphate, sodiumcarbonate, ammonia and combinations thereof.
 31. The method of claim 29or 30 further comprising washing the rinsed porous layer.
 32. The methodof claim 31 further comprising freeze-drying the washed porous layer.33. The method of any one of claims 24-32 comprising: at least partiallygelling a solution containing collagen; and applying the porous layeronto the at least partially gelled collagen solution.
 34. The method ofany one of claims 24-33 comprising: attaching the porous layer to anon-porous film comprising collagen.
 35. The method of claim 34 whereinattaching the porous layer to a non-porous film comprises adhering theporous layer to the non-porous film using chemical bonding,photoinitiation, surgical adhesives, surgical sealants, surgical gluesor combinations thereof.
 36. The method of claim 34 wherein attachingthe porous layer to a non-porous film comprises securing the porouslayer to the non-porous film using mechanical means selected from thegroup consisting of pins, rods, screws, staples, clips, sutures, andcombinations thereof.